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Introduction to Genetics

Introduction to Genetics

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Introduction to Genetics

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  1. Introduction to Genetics -the DNA molecule -nucleotides -chromosomes vs genes -DNA replication -cell division

  2. The DNA molecule • Composed of 2 polymers of nucleotides • Polymers are oriented in antiparallel • Molecule resembles a spiral staircase of complementary base pairs

  3. Nucleotide structure of DNA • Each nucleotide of DNA contains: • Deoxyribose • Phosphate • Nitrogen base (either A, G, C, T)

  4. Nucleotide structure of RNA • Each nucleotide of RNA contains: • Ribose • Phosphate • Nitrogen base (either A, G, C, U*) *contains Uracil instead of Thymine

  5. DNA structure • “Double helix” propsed by Watson and Crick (1953) • Antiparallel backbones • Complementary base pairing: • Adenine to Thymine • Cytosine to Guanine

  6. DNA structure

  7. Chromosomes vs Genes • A chromosomeconstitutes an entire DNA molecule + protein • Protein = histones • Supercoiled DNA in nucleosomes • Humans contain 46 such molecules (23 pairs) • 44 somatic chromosomes • 2 sex chromosomes (X +Y)

  8. Chromosomes vs Genes • Genes constitute distinct regions on the chromosome • Each gene codes for a protein product • DNA -> RNA-> protein • Differences in proteins brings about differences between individuals and species

  9. How do chromosomes become double stranded?Answer: DNA replication • During the life of the cell, each chromosome of DNA makes a copy of itself • This must occur prior to cell division to insure each daughter cell gets a complete set

  10. Therefore, prior to dividing, any cell must first replicate DNA • Each single-stranded (SS) chromosome duplicates to become a double-stranded (DS) chromosome • Example: • A human cell is formed with 46 SS chromosomes • Each chromosome replicates to produce 46 DS chromosomes

  11. DNA replication

  12. DNA replication occurs during the life of a cell = the Cell Cycle • DNA replicates (makes a copy of itself) to produce DS chromosomes • During this time, the cytoplasmic contents also duplicate • Spindle tubules form to aid in the process of cell division • Mitosis in body cells • Meiosis in sex cells

  13. The cell cycle